Many applications exist where humans may interact with lasers. Because lasers can generate large amounts of power, lasers can inflict harm to humans, especially to a person's vision. Lasers often have very low divergence and high coherence, which can cause retinal damage with exposure at even low power levels.
A safety class system is defined in ANSI Z136 and IEC 60825 and sets forth several classes of lasers for use in industry. The following descriptions of the various class designations are general in nature and are not meant to precisely explain the class designations defined in the ANSI and IEC standards, which may be updated from time to time.
In general, Class 1 lasers are defined to be safe under all conditions of normal use. For example, a continuous laser at 600 nm wavelength can emit up to 0.39 mW and may be considered a Class 1 laser. Other wavelength lasers may have higher or lower permitted power output to be considered Class 1, as different wavelength light is attenuated differently in the human eye.
In general, Class 2 lasers are more powerful than Class 1 lasers, but rely on a human's blink reflex to limit the exposure to less than 0.25 seconds and only apply to visible light lasers (400-700 nm). Class 2 lasers are generally limited to 1 mW continuous wave.
In general, a Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as from paper or other matte surfaces are generally not considered harmful. Within Class 3B, continuous lasers in the wavelength range from 315 nm to far infrared are limited to 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30 mJ. Other limits apply to other wavelengths and to ultrashort pulsed lasers. Protective eyewear is typically used where direct viewing of a class 3B laser beam may occur. Class-3B lasers generally are equipped with a key switch and a safety interlock.
In general, a Class 3R laser is considered safe when handled carefully, with restricted beam viewing. The Maximum Permitted Exposure can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are typically limited to 5 mW. Other limits may apply to pulsed lasers and lasers in other wavelengths.
In applications where a laser beam is used for detection, higher powered lasers may be desired so that the laser beam may be more accurately and effectively sensed. However, the more powerful lasers can inflict harm.